The present invention relates to a method of selecting among N “Spatial Video CODECs” where N is an integer number greater than 1, the optimum “Spatial Video CODEC” for a same input signal I. In this new technique (hereafter referred to as “Dynamic Coding”) for digital video coding, “Spatial Video CODEC” is understood as the combination of any transform of the input signal, followed by a quantization of the transform coefficients and a corresponding entropic coder.
Video Coding is an important issue in all application fields where digital video information has to be stored on a digital support or transmitted over digital networks. Several solutions have been proposed in the last 20 years and standardizations efforts have been undertaken to define a unified syntax.
Standard video coding schemes have a rigid structure. They take into account the context of specific, well-defined applications requiring video coding, and propose an optimized, albeit limited, solution. This explains the number of existing international recommendations that have been defined for specific applications. For example, the ITU-T H.261 standard is designed for tele-conferencing and video-telephony applications, MPEG-1 for storage on CD-ROM, MPEG-2 for wideband TV broadcast, MPEG-4 for low-bitrate coding with multimedia functionalities and H264 for very low bit-rate video coding.
The strategy adopted by classical video coding schemes is prompted by the fact that no a single universal coding technique can be applied with optimum results in every context. In fact, the performance of a “Spatial Video CODEC” depends on several application specific parameters, such as: the type of the data to be compressed (still pictures, video, stereo imagery, and so on), the nature of the visual data (natural, synthetic, text, medical, graphics, hybrid), the target bitrate, the maximum acceptable delay (ranging from few milliseconds to off-line), the minimum acceptable quality (spatial and temporal resolution), the type of communication (point to point, broadcast, multi-point to point, etc . . . ), and the set of functionalities required (scalability, progressiveness, etc.). Often these parameters such as the nature of the input signal or the available bandwidth may change in time with a consequent variation of the performances of the selected “Spatial Video CODEC”. In the following table, major specifications for a few of the most critical applications for video coding are listed. Reads “Mbps” Mega bit per second, “Kbps” kilobit per second, “fps” frame per second, “MP2MP” multi point to multi point, “P2P” point to point, “P2MP” point to multipoint
NatureTargetMaxMinimumType ofType of dataof databitratedelayqualitycomm.FunctionalitiesVideo SurveillanceLow_motionNatural3- 6Mbps300ms25- 50 fps,MP2MPFast frameVideoFULLaccessVideo telephonyStatic VideoNatural<500Kbps200ms10 fps,P2PScalabilityQCIFTelemedicineVideoHybrid>5Mbps<1sec50 fps,MP2MPScalability,Still_picturesTextFULLEditing, . . .Digital TVHigh_motionNatural,<1Mbps<1sec25 fps,P2MPRecord, fastVideotext,FULLframe accesssyntheticCorporate TVNaturalNatural,2Mbps<1sec50 fps,P2MPScalabilityText Synthetictext,FULLsyntheticVideo conferenceNaturalNatural,512Kbps<1sec25 fps,MP2MPScalabilityTexttext,QCIF-syntheticCIF
Given the wide variations in the requirements from application to application, it is clear that a coding scheme tuned for a specific application will be superior, for that application, to an universal coding technique that attempts to find a suitable compromise among different constraints. However, even the optimum “Spatial Video Video CODEC” for a specific set of constraints may be a sub-optimal solution when the parameters of the application are allowed to change through time. For example, in several multimedia scenarios, the video input combines static scenes to highly dynamic ones. Moreover, the sequences may be natural images, or synthetic scenes or combination of the two (text, graphs, and natural images) with a consequent variation of the statistical properties of the input signal.